Line Widths of Proton Magnetic Resonance Spectra of Proteins in Solution

The total line width at half height (Δvt) of proton magnetic resonances of proteins can be written as the sum of various terms, of which the most important is that due to the dipole‐dipole interaction of adjacent protons (Δ vdd) The contribution of Δ vdd to Δvt is calculated by an equation which includes the correlation time T c and the inter‐proton distance b. It is thus possible to explain the experimentally observed absence of C‐2 histidine resonances in a‐chymotrypsin and in some other native proteins and also the absence of S‐CH3 methionine resonances in all the native proteins examined except for a‐lactalbumin. On the other hand, if Δvdd and either T c or b are known, it should be possible to calculate the inter‐proton distance b or the correlation time T c respectively.